The activity and selectivity of some catalysts may be improved by fluorination of the catalysts. During fluorination the gaseous organic fluorine compound reacts with hydrogen and the catalyst with formation of the corresponding defluorinated organic compound, fluorinated catalyst and water. According to a process known from British Patent Specification No. 2,024,642 a gaseous organic fluorine compound is contacted in the reactor with the catalyst at elevated temperature and pressure, the reactor effluent gas being recycled and the duration of the injection of the organic fluorine compound into the gas being reduced to one impulsion.
According to the Examples described in this prior specification, the gaseous organic fluorine compound was injected in one second into the recycle gas at 150.degree. C. and after the recycle gas had been homogenized the temperature was gradually brought to 190.degree. C. The period required for homogenizing was less than one hour. This known process usually results in a generally uniform distribution of fluorine over the catalyst. In that specification, by a uniform distribution of fluorine over the catalyst is meant a distribution of fluorine in which the quotient of the fluorine content of the catalyst at the end of the catalyst bed (F.sub.2) and the fluorine content of the catalyst at the beginning of the catalyst bed (F.sub.1) may vary between 0.5 and 1.5.
It is an object of the present invention to achieve a still more uniform distribution of fluorine over the catalyst in a more practical manner.